Prospect of Magnesium Rich Rocks from Boula

Journal of Geosciences and Geomatics, 2014, Vol. 2, No. 5A, 7-11
Available online at http://pubs.sciepub.com/jgg/2/5A/2
© Science and Education Publishing
DOI:10.12691/jgg-2-5A-2
Prospect of Magnesium Rich Rocks from Boula-Nausahi
Igneous Complex, Odisha as Flux in Iron and Steel
Industry
S. Khaoash1,*, J.K. Mohanty2
1
Ravenshaw University, Cuttack
2
CSIR-IMMT, Bhubaneswar
*Corresponding author: [email protected]
Received November 01, 2014; Revised November 10, 2014; Accepted November 20, 2014
Abstract Rocks rich in magnesium hold good prospect as substitute flux for dolomite and limestone and quartz in
iron and steel industry. Our dependence on foreign imports, as far as raw materials like limestone or dolomite are
concerned, has nonetheless eroded the competitive ability of Indian iron and steel. The quality of raw materials used
determines to a large extent, the productivity and therefore utilisation of the capital assets in an integrated steel plant.
Scarcity of metallurgical grade limestone and dolomite especially of blast furnace (B.F.) and steel melting shop
(S.M.S.) grades have shifted focus to the quality and pricing of steel in India. The Boula-Nausahi Igneous Complex
of Odisha consists of ultramafic suite that includes dunite-peridotite-pyroxenite-lherzolite and their altered product
(serpentinite). These ultramafic rocks are enriched with high MgO and low SiO2 contents and very low Al2O3, Cr2O3
and alkalis contents.
Keywords: magnesium, flux, iron and steel industry, Boula-Nausahi igneous complex
Cite This Article: S. Khaoash, and J.K. Mohanty, “Prospect of Magnesium Rich Rocks from Boula-Nausahi
Igneous Complex, Odisha as Flux in Iron and Steel Industry.” Journal of Geosciences and Geomatics, vol. 2, no.
5A (2014): 7-11. doi: 10.12691/jgg-2-5A-2.
1. Introduction
Magnesian rocks as materials of economic significance
have caught the attention of the economic geologists,
metallurgists and industrialists the world over in recent
years. Though its development and utility as a commodity
of economic importance is still in nascent stage in India, it
holds good future prospect as substitute flux for dolomite/
limestone and quartz in iron and steel industry. Scarcity of
metallurgical grade limestone and dolomite especially of
blast furnace (B.F.) and steel melting shop (S.M.S.) grades
have put tremendous pressure on the quality and pricing of
the Indian steel.
Magnesian rocks viz., dunite, peridotite, pyroxenite etc.,
and their altered products (serpentinite) are found in some
well defined belts in India. Magnesian rocks are found in
the states of Tamilnadu, Odisha, Jharkhand, Karnataka,
Maharastra, Andhra Pradesh, Manipur, Nagaland and
Andaman & Nicobar Islands (IBM, 2012). In Jharkhand,
magnesian rocks are found in Jojohatu, Roroburu,
Chitungburu, Kittaburu, Kismiburu and Tilaisud. In
Karnataka, magnesian rocks are found in Sindhuvalli,
Talur, Koppal, Dodkanya, Dodkatur and Byrapur.
Bhandara district, Maharastra has good quality magnesian
rocks. Kondapalli hills located in the Krishna district of
Andhra Pradesh are made of ultrabasic rocks. In Andaman
& Nicobar Islands, magnesian rocks are found in
Badmash Pahar and Panchabati. Ophiolite Complexes of
Manipur, Nagaland and Ladakh are repositories of good
quality magnesian rocks.
In Odisha, Magnesian rocks are found in prolific
abundance. There are fourteen proven/ probable deposits
of which two are significant. They are the Sukinda
Ultramafic Belt and the Boula-Nausahi Igneous Complex.
The Sukinda Ultramafic Belt extends for over 20 km with
a width of 2-5 km. Though the Sukinda Ultramafic Belt is
the largest of its kind in India, its utility as a source of
magnesian rocks is very limited owing to the fact that the
most of the ultramafic rocks (dunite-peridotite) except a
few pyroxenite bodies towards the foothills of Mahagiri
Range have undergone extensive lateritisation.
The Boula-Nausahi Igneous Complex, a 3km long belt
extending in N-S to NNW-SSE direction, consists of
ultramafic, mafic and felsic rocks as major litho units. The
ultramafic suite includes dunite-peridotite-pyroxenitelherzolite and their altered product (serpentinite).These
ultramafic rocks are characterized by high MgO and low
SiO2 contents and very low Al2O3, Cr2O3 and alkalis
contents. These rocks disposed as wastes or at best used as
road metals have the potential to be used as substitute for
limestone/dolomite as flux in Iron and Steel industry.
2. Materials and Methods
A few samples were collected from the underground
mines and dump yards of Orissa Mining Corporation
8
Journal of Geosciences and Geomatics
(OMC) leasehold at Boula area, Keonjhar district. The
samples were collected after examining the degree of
alteration physically. These rock samples were studied for
petrographic
and
other
thermal
characteristics.
Petrographic study was carried out by optical microscope
(Leitz make). Bulk chemical analysis of the samples was
carried out by XRF (Philips, Magic Pro) on pressed pellets
by using international rock standards. LOI was determined
by heating the sample at 950°C for 2 hours. Thermal
properties were studied by Leitz Heating microscope.
3. Petrographic Characterisation
Magnesium rich rocks like dunite, peridotite,
pyroxenite, saxonite lherzolite, websterite, enstatitite,
serpentinite constitute the ultramafic domain of Boula
igneous complex. However, Dunite-peridotite represents
over 90% of the total ultramafic rocks.
Optical studies reveal that dunite consists of olivine and
+ accessory chromite. Peridotite consists of olivine +
Oxide
Wt%
SiO2
Al2O3
MgO
Fe2O3
CaO
Na2O
K2O
TiO2
Cr2O3
MnO
P2O5
LOI
MgO/SiO2
n= Number of samples
Dunite
n=7
41.81
0.69
45.00
2.48
0.030
0.003
0.002
0.02
0.31
0.06
0.002
9.02
1.076
enstatite + accessory chromite. saxonite consists of
enstatite + minor olivine + accessory chromite. In all these
cases, olivine is altered to serpentine and when the degree
of alteration is very high, the rock is converted to
serpentinite. Pyroxenite consists of enstatite + accessory
chromite. Diopside and hypersthene are the major
minerals in websterite. In some cases, pyroxenes are
altered to bastite and talc. Petrographically, the ultramafic
rocks and their altered products consist of olivine (+
serpentine), orthopyroxene (enstatite and hypersthene) and
clinopyroxene (diopside) in varying proportions with
minor to trace amounts of euhedral chromite and
secondary minerals. Lizardite is the major mineral in
serpentinite. The accessory chromite varies from 2 to 3%
in the ultramafic rocks.
4. Chemical Analysis
Major elements of different magnesian rocks are
analysed by XRF and the data are given in table below.
Table 1. Major element composition of ultramafic rocks
Peridotite
Pyroxenite
Saxonite
n=7
n=7
n=7
42.29
47.79
43.88
1.63
2.39
0.99
42.76
36.87
41.46
2.89
3.94
2.99
1.65
0.94
1.46
0.004
0.005
0.007
0.002
0.04
0.002
0.051
0.11
0.086
0.47
0.13
0.40
0.99
0.089
0.135
0.001
0.03
0.002
9.53
7.12
7.44
1.011
0.779
0.945
From the chemical analysis, it is observed that MgO
content varies between 45.00 & 36.87 wt%. SiO2 content
varies between 47.79 and 41.81 wt%. Al2O3 wt% varies
between 0.69 and 2.39 wt % and Cr2O3 between 0.13 to
0.49 wt%. Ca ranged between 0.21 to 1.65 wt% while
Na2O and K2O vary from 0.005 to 0.007 and 0.002 to 0.04
wt % respectively. There is no significant compositional
variation between serpentinite and dunite-peridotite
because serpentinite is a product of isochemical process
with addition of meteoric water only (Mohanty, 1994).
As the ultramafic rocks contain substantial amounts of
MgO and SiO2 and low alkalis, Cr2O3 and Al2O3, these can
be considered as substitute flux material for
limestone/dolomite and quartzite/sand in iron and steel
industry.
5. Utilisation
The liberalisation of the Indian economy in 1991
opened the flood gates of the closed door economy to a
market driven, forward looking one. Liberalisation has
brought about sea changes in technology based industries
like steel making and heavy engineering. An important
fallout of liberalisation is the intensification of
competition that necessarily influenced quality, pricing
Serpentinite
n=7
41.98
0.79
43.21
2.73
0.21
0.006
0.002
0.058
0.49
0.121
0.002
9.00
1.029
and better service to the customers. The advent of
liberalised economy has affected all walks of life and
almost all industries including iron and steel. This made
steel makers to look for improved technology and good
quality raw materials.
There is no doubt that the inferior quality of raw
materials is a major limitation in making the Indian iron
and steel industry globally competitive. For Iron and Steel
industry besides good grade iron ore, good quality fluxes
eg., limestone/dolomite and quartz are essential requisites.
Fluxes are raw materials used in furnace for removal of
undesirable impurities both at the iron and steel making
stages. To ensure smooth operation of blast furnace,
maintenance of low basicity is very essential. A low
basicity ensures better fluidity of the melt.
In India, the entire flux requirement in blast furnaces is
usually met out of limestone/ dolomite and silica. With
emphasis on higher productivity and superior quality, the
steel sector in India is beset with impediments to use
limestone containing high alkalis (>0.15%) and high silica
(>3%). The all India recoverable reserves of limestone and
dolomite are estimated at 75,660 Mt and 4,387 Mt
respectively (IBM, 2012). The limestone reserve in
Odisha stands at 1212 Mt and dolomite at 691 Mt. Most of
the Indian limestone and dolomite are of inferior grade,
falling short of BF and SMS specifications.
Journal of Geosciences and Geomatics
Looking at the present scenario, in order to maintain a
competitive edge iron and steel industries are forced to use
high quality limestone/dolomite or to find out a substitute
flux which can address the problem of inferior grade
limestone/dolomite found in the country. Import of high
quality limestone/dolomite will add to the cost of
production. So a frantic search for a substitute material is
on the threshold to be effectively used in place of
conventionally used fluxes. In this context magnesian
rocks stand a bright prospect. The present work gives a
detailed account of the various aspects of magnesian rocks
vis-à-vis their use in iron and steel industry.
6. Physico-Chemical Considerations
Physico-chemical and thermal characters of a raw
material are of paramount importance in determining its
suitability as a fluxing agent in Iron and Steel industry.
Physico-chemical considerations include entities like
silica, alkalis, LOI and other major oxide contents.
Besides these chemical parameters, sometimes the grain
size of the raw material also matters calling for due
attention.
Silica is used to obtain low blast furnace slag basicity.
Most of the silica input in blast furnaces under Indian
condition comes from coke and iron ore. Besides, an
additional silica input is obtained either from sand added
to sinter or quartzite charged directly into the blast furnace.
Addition of sand to sinter has its own attendant problems.
In Indian blast furnaces where high aluminous iron ores
are used, silica assimilation requires very high heat input
that affects both the sinter productivity and quality.
Quartzite when charged directly into the blast furnace
suffers from poor assimilation because of poor thermal
conditions prevailing in Indian blast furnaces (Mukherjee
et al. 1996). If there is no additional silica input into sinter,
the sinter basicity becomes very high (CaO/ SiO2 ≈ 3.0)
which gives rise to high temperature properties in terms of
poor softening-melting characteristics and high residuals
after melt down.
The role of the alkalis (Na2O and K2O) in determining
blast furnace performance cannot be undermined. These
alkalis contributed by the raw materials have an adverse
effect on blast furnace performance viz., decripitation of
the ore, decripitation of coke, erosion of refractory lining
causing hotspots and formation of scaffolds and hanging
of the overburden. The major sources of alkalis in blast
furnace under Indian conditions are from the high ash
containing coke and flux. The harmful effects of alkalis
can be minimised either by decreasing the alkali input into
the furnace or by removal of alkali through the slag.
At Tata Steel, a huge Indian Industrial conglomerate,
both lime and limestone are used as fluxing materials. The
ideal specification of limestone is CaCO3 >95%, Al2O3+
SiO2 <1% and Na2O +K2O <0.1%. The alkali content is
one of the deciding factors in the selection of fluxing
material. The need for lowering the alkali input to blast
furnaces had been so compelling that mining operations at
Birmitrapur and Hatibari quarries in Odisha were stopped
on account of their high alkali content (0.4%). Since it is
extremely difficult to remove the alkalis through slag in a
blast furnace, it is important to minimise alkali input into
the furnace by using low alkali raw materials instead of
high alkali ones.
9
In light of the above, it becomes imperative to select a
raw material which could decrease the sinter basicity
without increasing the heat requirement. Magnesium rich
rocks viz., dunite, peridotite, pyroxenite, serpentinite etc.,
could be considered as fluxes since they have appreciable
MgO and SiO2 contents with low or negligible alkali,
besides Al2O3 and Cr2O3 content within permissible limits.
The important considerations for a magnesian rock to be
used as a flux material are its high MgO, low Cr2O3
(< .5%) and Al2O3 (<1.0%) contents. Besides it should
have a low alkali content and low loss of ignition
(Chatterjee and Murty, 1998).
It is seen that the average crystal size of dolomite is at
least twenty times larger than that of limestone and 4-5
times larger than that of dunite. So, because of the
temperature conditions prevailing during sintering and the
short reaction time, limestone is more easily calcined than
dolomite and quickly assimilated into the melt. Dunite
requires no heat of calcination and gets easily assimilated
into the melt. Moreover, dolomite has higher LOI (4045%) content. As such more heat is required to expel CO2
during
calcination
process.
Thus
use
of
limestone/dolomite requires more heat energy in sinter
making. Dunite on the other hand has no carbonates and
has low LOI (7-10%) thereby saving in terms of energy.
Limestone and dolomite have obvious disadvantage
compared to dunite because of their sluggish and
incomplete assimilation of MgO. This gives rise to weak
areas in the sinter matrix that decreases the strength of the
sinter.
Chemical analyses of the ultramafic rocks show that,
these rocks are rich in magnesium (average MgO content
42%) and have a MgO/ SiO2 ratio ranging from 0.76 to
1.08. The oxides like Al2O3 and Cr2O3 that have a
deleterious effect on slag formation are present within
permissible limits except in pyroxenite. This
compositional problem can be overcome by a suitable
blending of pyroxenite with either serpentinite and / or
dunite (peridotite). Na2O content varies between 0.005 &
0.007 while the CaO content ranges from 0.95 to 1.41.
Another important consideration for flux selection is the
fouling index of the material.
Fouling Index (Rf) is given by = Base/ Acid* Na2O
Where
base =
Fe 2 O3 + CaO + MgO + Na 2 O + K 2 O acid = SiO 2 + Al2 O3 + TiO 2
Rf values for magnesian rocks of the area have been
found to be low i.e., between 0.005-0.007. This shows that
as far as fouling index is concerned, these rocks can form
good flux material. Fouling indices of dolomite and
limestone fluxes have been calculated to be around 1.095
and 0.748 respectively.
7. Thermal Behaviour
The thermal properties viz., surface tension, viscosity
and flow behaviour of flux material at high temperature
play significant role in determining the suitability of
fluxing agents. The thermal properties of the ultramafites
of the area have been studied using a heating microscope
to determine their suitability as flux materials in iron and
steel making.
10
Journal of Geosciences and Geomatics
The four deformation states of material during heating
operation are represented by ST, IDT, HT and FT. ST is
the softening temperature ie., when the sample just starts
softening due to a rise in temperature. Initial deformation
temperature (IDT) is the temperature at which the material
shows first sign of deformation like shrinkage, expansion,
decripitation etc. The HT (hemispherical temperature) is
the temperature at which the material assumes a
dome/hemispherical shape. The flow temperature (FT) is
the temperature at which the material behaves like a liquid
and starts flowing.
Viscosity of a fluid is defined as its property by virtue
of which it tends to oppose the relative motion between its
layers. Resistance to flow is largely due to inter molecular
attraction called the Vandar waals force. Slag viscosity
determines the flowability. Viscosity of a slag is
calculated by using the formula given by Watt and
Fereday (1969)
{
log viscosity = 107 m/ ( t-150 )
2
} +C
Where
m = 0.00835 SiO 2 + 0.00601 Al2 O3 − 0.109
C=
0.041 SiO 2 + 0.0192 Al2 O3 + 0.0276 Fe 2 O3
+0.016 CaO − 3.92
=
t 1400°C
The viscosity of the magnesian rocks varies between
1.70 and 5.00. Pyroxenite and saxonite show slightly
higher values. This low range of viscosity is attributed to
the complete melting of the flux at a temperature of about
1400°C. Sintering of magnesian rocks starts within 700 1180°C and the fluid phase is attained at a higher
temperature of 1400°-1600°C. Using the formula of Watt
Rock types
Dunite
Peridotite
Pyroxenite
Saxonite
Serpentinite
ST
1050
1090
1100
680
700
and Fereday, viscosity of dolomite and limestone has been
calculated to be 7.0 and 9.4 respectively.
Often the slag sticks to the inner linings and walls of
the boiler/ furnace which can impair the efficiency of the
furnace. Sticking of slag to the linings is governed by the
surface tension.
Surface tension of slag produced from magnesium
rocks has been calculated using formula given by Holy et
al., (1965).
ρ = 3.24SiO 2 + 5.85Al2 O3 + 4.4Fe 2 O3 + 4.92CaO
+5.49 MgO + 1.12 Na 2 O − 0.75 K 2 O
The surface tension for different magnesian rocks has
been calculated to be around 400, thereby minimising the
possibility of the slag adhering to the inner lining of the
boiler. Surface tension reduces the area of a surface to
minimum. It is due to this, that small drops of liquid or
bubbles are spherical in shape. This is because, for a given
volume a sphere has minimum surface area. So, the
separation between the slag and the metal will be easier.
The higher values are attributed to the complete melting of
the flux. Dolomite and limestone on the other hand have a
surface tension of 275.85 and 294.95 respectively which is
considerably lower than the magnesium rich rocks.
Slagging index, another temperature dependent parameter
also determines the suitability of the flux material. It is
expressed as Rs and calculated using the following
formula.
Slagging index,
=
Rs
8. Conclusion
The different types of magnesium rocks encountered in
this complex include dunite, peridotite, pyroxenite,
+ 4 min.IDT ) / 5
Slagging index for the different magnesian rocks is
found to be very low ie., varying between 1140 to 1326°C.
Table 2. shows the thermal properties and fouling
indices of the magnesian rocks.
Table 2. Thermal properties of magnesian rocks
IDT
HT
FT
Rs
1250
1350
1390
1270
1300
1430
1500
1326
1130
1180
1290
1140
1150
1280
1450
1176
1040
1370
1480
1106
From the above data, it is inferred that these magnesian
rocks exhibit excellent thermal properties like narrow
range of temperature between HT and FT, low viscosity
and slagging behaviour. The softening and melting
temperature is narrow in case of dunite. Magnesian rock
sinters have higher reducibility and hence the efficiency of
an equal volume of magnesian rocks as compared to that
of dolomite sinter is substantially more (Mukherjee et al.
1996).
So, by all benchmarks (physico-chemical and thermal
considerations), magnesian rocks perform better as flux
materials compared to limestone/dolomite and quartzite.
Hence magnesian rocks can be used effectively as better
quality flux leading to improved productivity
(output/input) and substantially curb import of high
quality fluxes.
( max.HT
V
1.7
3.73
5.0
4.91
1.74
ρ
397.61
402.15
393.18
395.93
390.81
Rf
0.003
0.004
0.004
0.007
0.006
lherzolite, saxonite, websterite and serpentinite. MgO
content in the above rock types varies between 36.8 to
45.00 wt% whereas SiO2 varies between 41.81 to 47.79
wt%. Al2O3 wt% varies between 0.66 and 2.35% and
Cr2O3 between 0.11 to 0.50 wt%. Na2O and K2O vary
between 0.005 to 0.007 and 0.002 to 0.04 wt %
respectively.
With very good thermal properties coupled with desired
chemical parameters, magnesian rocks can make good
substitutes for dolomite/ limestone and quartzite as flux
materials. Magnesian rocks do not require any heat of
calcination. These get easily assimilated into the melt and
therefore require less heat energy. Assimilation of
limestone/dolomite and quartzite, on the other hand, is
heat intensive and time consuming as well. Often
unreacted portions are left behind, which decrease the
strength of the resultant sinter. The problem is further
compounded and accentuated by scarcity of appropriate
grade of limestone/dolomite and other economic aspects
viz., transportation, distance of the smelter from the mine
head etc.
Journal of Geosciences and Geomatics
Acknowledgement
[3]
The authors are grateful to the Director, IMMT for kind
permission to use the laboratory facilities during the work.
[4]
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